Carbon and oxygen are converted into nickel
in a white dwarf through a complex network of reactions.
The incremental changes tend to follow the series of atomic
nuclei that are multiples in composition of the helium
nucleus.  For this reason, large amounts of neon-20,
magnesium-24, silicon-28, and other elements with equal
and even numbers of protons and neutrons are created.  But
the reactions also tear down nuclei, creating many free
protons, neutrons, and helium nuclei that combine with
other atomic nuclei to produce elements and isotopes
that do not have equal numbers of protons and neutrons
or do not have an even number of protons or of
neutrons.  Because thermonuclear fusion disrupts
a white dwarf, the thermonuclear reactions in
a white dwarf  contribute to the rich variety
of chemical elements and isotopes we find throughout
the universe.